o Only two visitors will be permitted per patient in a patient room at one time.

New York State Health Commissioner Nirav Shah said Thursday that more than 19,000 flu cases have been reported this year, compared to just over 4,000 last year.

Shah said two children died from the flu in New York and it's not too late to get shots to protect against the disease.

From the Rocky Mountains to New England, hospitals are swamped with people with flu symptoms. Like Saratoga Hospital, other medical centers also have limited visitors. Other hospitals' visitation rules include requiring family members to wear masks and banning anyone with flu symptoms from maternity wards. One Pennsylvania hospital set up a tent outside its ER to handle feverish patients.

Flu usually doesn't blanket the country until late January or February, but it is already widespread in more than 40 states. Whether this will be considered a bad season by the time it has run its course in the spring remains to be seen.

What may complicate the situation is that the main influenza virus this year tends to make people sicker, and there are other bugs causing flu-like illnesses. So what people are calling the flu may, in fact, be something else.

"There may be more of an overlap than we normally see," said Dr. Joseph Bresee, who tracks the flu for Centers for Disease Control and Prevention.

The flu's early arrival in the U.S. coincided with spikes in a variety of other viruses, including a childhood malady that mimics flu and a new norovirus that causes what some people call "stomach flu."

Most people don't undergo lab tests to confirm flu, and the symptoms are so similar that it's sometimes hard to distinguish flu from other viruses or even a cold. Over the holidays, 250 people were sickened at a Mormon missionary training center in Utah, but the culprit turned out to be a norovirus, not the flu.

Flu is a major contributor, though, to what's going on, doctors say.

On Wednesday, Boston declared a public health emergency, and all the flu activity has caused some to question whether this year's flu shot is working.

There's a new flu vaccine each year, based on the best guess of what flu viruses will be strongest that year. This year's vaccine is well-matched to what's going around. The government estimates that between a third and a half of Americans have gotten the vaccine.

But the vaccine isn't foolproof, and even those who were vaccinated can still get sick. At best, the vaccine may be only 75 percent effective in younger people and even less so in the elderly and people with weak immune systems.

Health officials are analyzing the vaccine's effectiveness, but early indications are that about 60 percent of all vaccinated people have been protected from the flu. That's in line with how effective flu vaccines have been in other years.

On average, about 24,000 Americans die each flu season, according to the CDC.

Flu usually peaks midwinter. Symptoms can include fever, cough, runny nose, head and body aches and fatigue. Some people also experience vomiting and diarrhea, and some develop pneumonia or other severe complications.

Most people with flu have a mild illness and can help themselves and protect others by staying home and resting. But people with severe symptoms should see a doctor. They may be given anti-viral drugs or other medications to ease symptoms.

The last bad flu season involved a swine flu that hit in two waves in the spring and fall of 2009. But that was considered a unique strain, different from the regular winter flu.